Known as an X-ray analysis technology in a nanometer-scale region is a S(T)EM-EDX or a S(T)EM-WDX for scanning a sample with use of an ultra-micro electron probe and dispersing an X-ray generated from a local region irradiated with an electron beam (SEM: Scanning Electron Microscope, STEM: Scanning Transmission Electron Microscope, EDX: Energy Dispersive X-ray Spectroscopy, and WDX: Wavelength Dispersive X-ray Spectroscopy). The S(T)EM-EDX or the S(T)EM-WDX is an apparatus in which the S(T)EM is equipped with an energy dispersive X-ray spectrometer (EDX) or a wavelength dispersive X-ray spectrometer (WDX).
In the EDX spectrometer, a lithium drifted silicon semiconductor detector or, in recent years, a silicon drift detector (SDD) is used as a detector, and by dispersing a pulse signal generated by the semiconductor detector with use of a multi-channel pulse-height analyzer, parallel detection is enabled. In the WDX spectrometer, a diffraction grating for monochromating the X-ray and a detector for detecting the monochromated X-ray are used, and serial detection is performed in which the diffraction grating and the detector are operated. The WDX spectrometer has an energy resolution of several eV to several tens of eV, which is one or more digits higher than that of the EDX spectrometer, which is 120 eV.
The WDX spectrometer is a detector in which a diffraction grating serving as a diffraction grating is operated based on Bragg diffraction shown in Equation (1). In the equation, d is crystal lattice plane spacing of the diffraction grating, θ is an incident angle of the X-ray in the grating surface, n is a diffraction order, and λ is a wavelength of the X-ray.2d sin θ=nλ  (1)
The WDX spectrometer is generally categorized into two types. One is a type of dispersing and detecting an X-ray while rotating a multilayered flat-shaped diffraction grating 113a and operating a WDX X-ray detector 114 as illustrated in FIG. 2. The WDX spectrometer of this type turns an X-ray entering the flat-shaped diffraction grating 113a into a parallel X-ray 134a. Also, to improve a yield of an X-ray 134 generated from a sample 129 by irradiation with a primary electron beam 128, an X-ray condensing lens 112 is installed between the sample 129 and the flat-shaped diffraction grating 113a (e.g., PTL 1). To turn the X-ray 134 entering the flat-shaped diffraction grating 113a into the parallel X-ray 134a, a slit is installed between the sample 129 and the flat-shaped diffraction grating 113a in some cases. The other is, as illustrated in FIG. 3, a type of including a curved diffraction grating 113b called Johann or Johansson geometry and the WDX X-ray detector 114 and dispersing and detecting an X-ray while operating the curved diffraction grating 113b and the WDX X-ray detector 114 on a Rowland circle.
The WDX spectrometer in principle detects higher order X-ray in which n shown in Equation (1) are two or more as well. Since the spectrum of the higher order X-rays may overlap with a spectrum that is desired to be measured, which may cause a false detection. To prevent the false detection caused by the higher order X-rays, pulse-height distribution data shapes are distinguished from each other with use of an energy difference between the X-rays entering the WDX X-ray detector 114 (e.g., PTL 2).
As for detection of a light element in the above EDX and WDX spectrometers, in recent years, the EDX spectrometer dispenses with a detection window to prevent the window material from absorbing an X-ray of the light element, and the detection sensitivity of the light element is improved. However, since the EDX spectrometer has as a low energy resolution as 120 eV, in detection of a B (boron) element, for example, a tail part of a Carbon(C) X-ray peak as a C contamination generated by irradiation with an electron beam overlaps with a Boron X-ray peak, and the minimum detection sensitivity is thus about 10%.
In detection of a light element in the WDX spectrometer, a window material of the spectrometer is thinned to restrict absorption of an X-ray of the light element into the window material. In addition, by using an X-ray condensing lens formed in a shape contributing to an increase of the collection rate of the X-ray of the light element, the detection sensitivity of the light element is improved (PTL 3). Since the energy resolution of the WDX spectrometer is one digit higher than that of the EDX spectrometer, the overlap of the tail of the C peak with the B peak, which has been a problem in the aforementioned EDX spectrometer, is drastically decreased, and the WDX spectrometer can detect B of less than 1% except detection of a light element in a heavy element.